1. Field of the Invention
The present invention relates first of all to a system for exchanging information between at least one portable object and at least one sedentary exchange device.
Such a system applies particularly in the locksmithing field. In this case, the portable object is a key provided with electronic circuits capable of receiving, storing and transmitting information in the form of electric signals, and the exchange device is disposed on a lock. The exchange device is adapted for reading, at the moment when the key is introduced into the lock, a secret identification number stored in this key, and for preventing unlocking of the lock if this identification number is not correct. Such a system may be installed on a lock and a key of conventional type, i.e. comprising already a purely mechanical device for identifying the key, so as to reinforce the safety offered by this device. On the other hand, such a system may also be installed on a lock and a key not comprising any mechanical identification means, if the safety thus obtained is considered sufficient.
2. Description of the Prior Art
Systems of the above defined type are already known described for example in German applications DE-A 35 07 871 and DE-A-28 02 472 or in the European application EP-A-0 223 715. In all these systems, the information exchanges between the key and the exchange device take place through a plurality of conductors. This requires, on the lock, a connector provided with a plurality of contacts to be accurately positioned with respect to the contacts of the key, which sometimes raises problems, particularly because of the small size of the key. Furthermore, this makes it impossible in practice to construct a system in which the key and the exchange device are coupled, without electric contacts, by replacing each of the conductors by a pair of two antenna, to the extent that it is very difficult to readily house in a key a plurality of antennae, while taking care that in addition none of them picks up, as a whole or partially, a signal intended for the others. Now, a system without electric contacts has, in some cases, advantages, such as insensitivity to stains, or the possibility of mechanically protecting the key by a plastic material molding.
A system is also known from the French patent FR 2 180 349 in which the information exchanges between the key and the lock take place through two conductors only, one for setting a common reference potential and the other for transmitting potential variations in one direction or in the other. However, this result is obtained at the price of a relative complexity of the signals and processing circuits, which complexity results in the fact that, if attempts are made to omit these conductors, it is necessary to provide two pairs of antennae, one for the passage of signals from the exchange device to the portable object and the other for the passage of signals from the portable object to the exchange device.